transformers-0.3.0.0: Concrete functor and monad transformers

Portability	portable
Stability	experimental
Maintainer	ross@soi.city.ac.uk
Safe Haskell	Safe-Infered

Control.Applicative.Lift

Contents

Collecting errors

Description

Adding a new kind of pure computation to an applicative functor.

Synopsis

data Lift f a
- = Pure a
- | Other (f a)
unLift :: Applicative f => Lift f a -> f a
type Errors e = Lift (Constant e)
failure :: Monoid e => e -> Errors e a

Documentation

data Lift f a Source

Applicative functor formed by adding pure computations to a given applicative functor.

Constructors

Pure a

Other (f a)

Instances

Functor f => Functor (Lift f)

Applicative f => Applicative (Lift f)

A combination is Pure only if both parts are.

Foldable f => Foldable (Lift f)

Traversable f => Traversable (Lift f)

Alternative f => Alternative (Lift f)

A combination is Pure only either part is.

unLift :: Applicative f => Lift f a -> f aSource

Projection to the other functor.

Collecting errors

type Errors e = Lift (Constant e)Source

An applicative functor that collects a monoid (e.g. lists) of errors. A sequence of computations fails if any of its components do, but unlike monads made with ErrorT from Control.Monad.Trans.Error, these computations continue after an error, collecting all the errors.

failure :: Monoid e => e -> Errors e aSource

Report an error.